A separately-excited DC-DC converter is a device for converting an input DC voltage into an output DC voltage with a magnitude different from the input DC voltage, in response to a drive pulse signal having a predetermined repetition frequency.
Various types of separately-excited DC-DC converters have been developed, one type of which includes a switching circuit from periodically interrupting the input DC voltage in response to the drive pulse signal. The interrupted DC voltage is supplied to a transformer which raises or reduces the voltage of the input DC voltage. The thus transformed voltage is further transformed, if desired, and then rectified by a rectifier which is preferably a full-wave rectifier. The rectified voltage is smoothed by a smoothing circuit into the DC output voltage.
Such DC-DC converter as mentioned above is advantageous in that the repetition frequency of the interruption therein can be relatively freely changed by selecting the repetion frequency of the drive pulse signal. However, it has been a problem that an undesirably large intensity of a primary current flows in the transformer at no-load or light load conditions, thereby causing large loss of electric power.
Accordingly, it is a primary object of the present invention is to provide an improved separately-excited DC-DC converter which is free from such problem as mentioned above and having a less magnitude of loss of power under a no-load or light load condition.
It is another object of the present invention to provide a separately-excited DC-DC converter which can stably operate notwithstanding fluctuation of load.
It is a further object of the present invention to provide a separately-excited DC-DC converter which can stably operate even under large variation of the ambient temperature.
Other and more particular objects and advantages will be apparent from the following description taken in conjunction with the appended drawings wherein like reference numerals refer to like parts.